One or two (depending on whether you buy the 16 GB or 32 GB kit) PC4-21300 16 GB RAM chip
iFixit opening tool
Precision bit driver
4 mm precision bits required for the job (Torx T5, Torx TR6, and Torx TR10)
iFixit's tools are some of the best available -- I know, because I use them every day! -- and will make the upgrade process as smooth and as painless for you as possible.
This means that if you have a 2018 Mac Mini with the base 8 GB of RAM, you can upgrade to 16 GB for only $165, compared to the $200 Apple wants for the extra RAM. And as a bonus, you can also make use of one of the 4 GB RAM modules, which means you end up with 20 GB of RAM!
My ZDNet colleague David Gewirtz carried out this upgrade, and documented the process (even publishing a video) explaining how to do it. However, note that Gewirtz is very experienced when it comes to carrying out hardware upgrades, and he describes the process as "a tiresome and fiddly process that's not for the faint of heart."
You have been warned!
Must-have tools you need for repairing PCs, smartphones, tablets, and much more